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Troubleshooting help with a single-phase 5Hp motor/compressor

Good evening and Happy New Year to all.

I am trying to find the cause for the overheating of a 5 HP single phase motor which turns a belt driven refrigeration compressor. The FLA at the plate reads 21.5 amps, while the running amps in my meter never read above 21.0 amps.
The motor does not run continuously: it has a thermostat controlled pumpdown type control system, cycled by the low pressure control. Nevertheless, as the motor runs for a few hours, it becomes hotter and hotter until the thermal protector opens. I already replaced both the start and run capacitors. One thing I did notice is that this is a 230 volts motor, not the regular 208/230 volts, but the line voltage stays between 208 and 210 volts. It had been working without trouble for 5 years. Never re-wound before. What do you thing?

Sounds like possible motor problem, if it is drawing .5 amps below full load amps at 210v then at 230v it would be over amping. The average running amps should never be that close to fla or it will over heat. What about bearings or belt tentionas jaypslugger mentioned?

Every time that motor overheats and opens the thermal protector the insulation on the run windings becomes a little more degraded. If you didn't need a new motor when this all started you do now. Chances are a partial short circuit in the middle of the run winding started the overheating condition, which is now getting worse. Single phase is not as torqey as 3 phase, but you got what you got! Try to get a 208/230 motor next time. I agree with JJ could also be the compressor getting tired.